Typical physical networks include many routers and switches through which packets travel. In some cases for such networks, an administrator may identify that packets are not being delivered correctly, and therefore may wish to troubleshoot the network. In order to do so, some physical networks have the ability to perform a route trace that shows how far a packet travels. In physical networks, the administrator can often log into the routers and troubleshoot the routing table.
However, in at least some virtualized networks that operate many separate logical networks over the physical network, packets are typically sent across the physical network in tunnels between managed forwarding elements. These tunneled packets are passed through the unmanaged physical forwarding elements (e.g., standard routers) with minimal processing, and inspecting the routers will not provide an administrator with useful information. Thus, methods for troubleshooting virtualized networks are needed.